Modern electronic equipment uses digital semiconductor integrated circuits for operation thereof. The digital semiconductor integrated circuits receive inputs from various sources, e.g., pushbuttons, sensors, etc., and have outputs that control operation of the equipment based upon the various inputs thereto. The inputs and outputs of the semiconductor integrated circuits may be subject to undesirable high voltage electrostatic discharge (ESD) in addition to the desired input or output signal level. The ESD, characterized by fast transient high voltage discharges, may be from static electricity generated by a user of the equipment, equipment handling, power supply voltage transients and the like.
Semiconductor integrated circuits are becoming functionally more capable and are operating at faster speeds. The increased functional capability is the result of higher transistor count in each integrated circuit, thereby allowing the operation of more sophisticated software and/or firmware to produce the many features available in the equipment. The faster operating speeds further enhance the operation of the equipment. In order to keep integrated circuit die size within a reason cost, the electronic circuits therein must be more densely concentrated in as small an area as possible, thus the many transistors making up the electronic circuits within the integrated circuit must be made as small as possible. As these transistors become smaller and smaller, the spacing of the parts of each transistor, e.g., source, gate, drain, becomes smaller, as does the dielectric thickness of the insulation between these parts. The extremely thin dielectric is very susceptible to damage by excessive voltages present in an ESD event. Also, as operational speeds increase, the need for low capacitance structures becomes more important.
Various voltage protection circuits have been used to limit the peak voltage at an input and/or output of an integrated circuit. Attempts have been made to incorporate ESD protection within the integrated circuit, but are not very effective and/or require a significant amount of area within the integrated circuit die, and may add unacceptable additional capacitance to the circuit node being protected.
Therefore, what is needed is an ESD protection circuit integral within the integrated circuit die that is effective is protecting sensitive input and/or output circuits and has low capacitance.